The present invention relates to rotating electrical machines (e.g., electrical motors and generators) and in particular to a rotating electrical machine employing axially extending pegs.
Electrical motors and generators share similar structures of an electrically interacting stator and rotor and may be collectively termed “rotating electrical machines.” Conventional rotating electrical machines may be roughly divided into “electromagnetic” devices exploiting magnetic fields between moving parts, and “electrostatic” devices exploiting electrical fields between moving parts.
Electrostatic rotating electrical machines have a number of advantages over conventional electromagnetic rotating electrical machines including the elimination of magnets and costly rare earth materials, significant weight from ferrous materials, and high current copper windings. Electrostatic machines may be made of lower weight/cost dielectric materials and conductors.
Electrostatic machines are commonly found in micro-scale, micro-electromechanical systems (MEMS) which permit extremely small, gaps between rotor and stator elements allowing high capacitance between surfaces and high electrical fields. For larger scale rotating machines, for example, those providing integer horsepower and larger outputs (macro-scale), the physical gap between the stator and rotor may be one to three orders of magnitude larger than that for MEMS machines. This larger gap requires higher applied voltages typically in the thousands or even tens of thousands of volts for comparable shear stress (electric field strength) in the rotor/stator gap to attain useful amounts of torque. These high voltages normally require ultrahigh vacuum containment vessels to prevent arcing between stator and rotor components. The simultaneous requirement of minimizing the gap (tolerances) between stator and rotor components and using high voltage driving power, in macro-scale rotating machines, can present significant manufacturing challenges in manufacturing macro-scale electrostatic motors.
U.S. patent application Ser. No. 14/598,411, assigned to the assignee of the present invention and hereby incorporated by reference, describes an electrostatic rotating machine that simplifies manufacture by eliminating plates in favor of interdigitated pegs immersed in a high dielectric strength, high relative permittivity fluid. The peg-style construction allows increased design flexibility through modification of peg spacing alignment and dimensions, allowing variations in capacitance as a function of rotation to be maximized and closely matched with available driving voltages/currents for improved torque and torque consistency. Torque is generated in the reference patent by means of variable capacitance. As the shaft of the machine turns, the capacitance among the rotor and stator pegs varies, Applying voltage to specific pins sets will produce torque proportional to the derivative of the capacitance with respect to position. This torque mechanism is the dual to electromagnetic reluctance based machines.